"can see" is used (usually) when something is in front of your eyes, or being pointed at (as in "we can see that the red line goes above the blue one"). In Hebrew can see could be translated to יכולים לראות / ניתן לראות to convey that meaning ("ניתן לראות שהגרף ארוך").
Furthermore, to convey that exact nuance, I would've used "כאן", as in "כאן אתם יכולים לראות ..."
But the correct translation of the plain use of לראות is a plain "see". E.g., מה אתה רוצה לראות? what would you like to see? אני רואה אותו כל יום I see him on a daily basis. (cf. I can see him on a daily basis, which has a completely different meaning in both languages).
The verb "to see" is not usually used in continuous tenses. If it is, it usually means "to date, to go out". That was your mistake. The word "can" can be there, but it is not mandatory. Example:
John sees Lilly. (it means that John is looking at Lilly).
John is seeing Lilly. (it means that he is dating, going out with Lilly).
If we were to add "can" here, to make it: John can see Lilly. (at least to me that would mean either "he is able to see her" or that there was an obstacle in their way that has gone away and now "he can see her".
So, both with or without "can" mean the same thing, there is just a small nuance, whereas there would be a very big difference between "sees" and "is seeing".
I agree with your general point, but I think that his sentence should have been accepted as an indication that he understood the Hebrew. No one would interpret his sentence to mean "we are dating a black rabbit"; and there are other perfectly reasonable uses of the present continuous form of the verb "to see".
- Are you seeing what I'm seeing?
- Yes, I think we are seeing the rare black hare.
- I thought I'd have to tell my doctor that I'm seeing spots before my eyes.
This course is inconsistent in many ways, including when it accepts an answer in the simple present tense and when it accepts an answer in the present continuous.
I do agree, though, with everything else you said.