"This television is low."
A television could, I suppose, be short if it had odd dimensions. If the screen was very wide but little height, you might say it was short. As far as low, I agree it is basically meaningless in English. Maybe if the tv was on the floor and couldn't be viewed easily, but then I think you'd have to say that it's "too" low.
It can sometimes refer to the volume moreso than the TV itself, as a figure of speech called a synecdoche. If someone were to say that a TV is low, it's likely that the intended meaning is that the volume is low, similarly to how someone might say "Turn the TV down."
They wouldn't be telling you to literally point the TV downwards.
You are correct This is not a sentence that is said in english. The correct sentence would be "This television is too low". OR "This television is placed very low on the wall". So It is very obvious that the person who made the sentence "This television is low" is NOT a native english speaker. I hope they fix it. I hope that helps.
I'll register my common rant that my translation is not 'wrong' if I drop the 'この'. If I say テレビは低いです then it's implied that 'this' television is low. I get this wrong every time because I speak conversation Japanese and am like 'literally nobody cares if you have the 'この' or not... it's assumed knowledge that you're talking about the immediately visible TV.