Don't - don't, don't, don't - go to Wikipedia for insight. Wikipedia is not an academically respectable source, as your institution should itself have told you. It is shot through with mistakes. Nothing on there is subject to proper peer review. If you are at a university then read from proper peer-reviewed sources - that is, academic articles and books by respectable academic presses (not books by philosopher-wannabes with no academic credentials in the area).
As for the distinction in question, deontology is the name of a family of views of which Kantianism is a variety. So, Kantians are deontologists, but a deontologist is not necessarily a Kantian. (And Kant's own ethical theory would be a variety of Kantianism).
Crudely, actions can be said to have three components - the agent, the act itself, and the act's consequences. And the three major approaches to ethics - virtue ethics, deontology and consequentialism - can then be understood as trying to ground our moral duties in one or other of those components. Virtue ethicists ground our duties in qualities of the agent, deontologists ground our duties in the nature of the act itself (so they differ from virtue ethicists in that a virtue ethicist would say that Xing is right because it manifests a virtue, whereas the deontologist would say Xing is right and so that's why performing it is virtuous), and consequentialists in the consequences of the act (xing is right because it has good consequences, and a virtuous person is someone who typically performs acts that have good consequences).
A Kantian is a deontologist who says something more specific about the nature of those acts that are wrong. But Kantianism itself denotes a family of views all of which analyse the wrongness of wrong acts in terms of them manifesting one or other of a certain cluster of features - such as, for example, being an act that treats others as mere utensils because they are acts that could not be consented to by a rational deliberator, or being an act that the agent him/herself would not have agreed to under a range of circumstances, and so on. They basically seek to ground the wrongness of an act in something to do with the autonomy and consent either of the agent or of others.
But by no means all deontologists would take themselves to be restricted to analysing the wrongness of wrong acts in this way. A good example of a deontologist who is not a Kantian would be W.D.Ross. This has become too long, but to give an example of a way in which one might be a deontologist, but not a Kantian, take breaking promises.
Ross thought that acts of promise breaking are prima facie - that is, default - wrong. But he didn't think we need to say any more about why they are wrong. They are wrong because they are wrong. It is just the nature of acts of promise breaking that they are prima-facie wrong. (Ross, who was an expert on Aristotle, was no doubt influenced in his ethical thinking by Aristotle's dictum that it is unwise to try and explain the more obvious in terms of the less - it is more obvious that breaking one's promises is wrong than that it is wrong for this or that reason, and thus the wise person does not seek to analyse why promise breaking is wrong but just accepts its wrongness as a basic atom in the moral, er, molecule).
A typical Kantian, by contrast, would seek to explain the wrongness of promise breaking in terms of it being an act that expresses a policy that we could not agree to everyone else acting on, or in terms of promise-breaking being something that the affected party could not have agreed to, etc.