They may be strict because on top would be 上面 instead of just 上.

No, I think "on" is the usual expression in this context for most English speakers. "on top of" is normally only used instead of "on" when there is another possible position that the first object can have in relation to the second and the "top of" provides clarification e.g. You can be on the mountain but not on top of it, or on the bus but not on top of it. However with the coffee's position in relation to a table the only normal position is "on" it, so it is not necessary to say "on top of", and most people will not say that as there is no other valid position the coffee can take, so further clarification is not required.

Of course "on top of" is not actually wrong, and those who think that that is what they would normally say in this context could try reporting it.

15 nov 2018

Covfefe?

I think that is a fine translation, but on second thought that sentence is more passive English. So they probably would want a more passive Chinese translation.