English is remarkably plastic. One can wrench many seemingly ungrammatical statements into line by providing suitable context or by specifying an unusual point of view.
In your fellow-teacher’s example, we could posit this hypothetical context:
- he (or any pronoun you prefer) is as rich as Bill Gates, and has been for a long time;
- he experienced a significant change, such as becoming a lot more calm or frantic, or generous or miserly, or perhaps found faith, etc;
- the speaker is amazed at the change, thinking that such a change is unheard of in a man of wealth.
The speaker then expresses that amazement by asking the question your fellow-teacher approved. The change is in the past, and the wealth is in the ‘timeless’ or ‘continuing’ present, so the question correctly expresses the speaker’s intent.
With that same context, your alternative wouldn’t express the speaker’s intent.
However, because there is some conceivable context for each question that validates that question, both questions are grammatical.
Instead of asking whether the bare question of whether a sentence is correct, it might be more useful to have the student or teacher express the context (using any convenient language), and then ask whether the English sentence fits that context.