This is a good question. Some bandejas will be hit high, some others lower. The bandeja is just a "desperate" defensive shot in which you are trying not to lose the net because the lob of your opponent was good.
And in real life the vibora will also not always be the same since you will execute this shot when the lob is good enough not to be smashed, but not THAT good so that it forces you to play a bandeja. Vibora is faster, and bounces lower. And like I said there are different lobs and situations depending on how close you are to the net, etc.
I don't think your trainer is right to be honest. Bela was known for having the best bandeja 5-10 years ago, and it was a pretty high flat fast bandeja that went straight to the opponents feet. So these shots are not always the same.
The main thing to understand is the difference in their nature. Bandeja is a more defensive/desperate shot done when the lob is good, vibora is a more offensive shot used when the lob is not that good. If you are Bela maybe your bandeja can be quite special and be hard to defend as well and be kind of offensive. But the main goal of the bandeja is to not lose the net and executions may vary. You hit the bandeja from around the line, and you run back to the net to volley / block the next shot.
Edit: even Bela himself here says "bandeja should be hit at shoulder height" and then proceeds to do some bandejas and look how high he is hitting. Like a meter above his shoulder hehe. So, take with a grain of salt these things they say. [https://www.youtube.com/watch?v=uGaxCwnIOq0](https://www.youtube.com/watch?v=uGaxCwnIOq0)
https://preview.redd.it/7fxmpwzgk41h1.png?width=1816&format=png&auto=webp&s=51472bb97335256072198e553709a8445c7ce116
Now here, Lebron hitting a bandeja.
[https://www.youtube.com/shorts/MCkeXOevlCM](https://www.youtube.com/shorts/MCkeXOevlCM)
Again, half a meter above the head...
I think those clips might be causing you some unnecessary complexity. Neither of those is truly a bandeja despite their titles. Bela is hitting a gancho to the fence from a disguised preparation, probably to surprise opponents who are tempted to come up and volley his actual bandeja. Lebron is doing something similar, but he's actually disguising an amago to the middle with a fake a gancho to the fence from a disguised vibora preparation that's just obvious enough to draw his opponent to the left side of the net. Levels of mind games that are far beyond what any of us needs, and impact technique in what look like non-optimal ways.