That appears to be constructed in order to deceive though.

Someone who was thinking about a problem and drawing something would always with a drawing like that either intend the angle to be the same, or otherwise highlight the fact that one triangles is 8/3 and the other is 5/2 so that the slope is obviously not the same.

Good visual proofs simply use lines and figures to talk about actual algebra instead of symbols; but every outcome is still in a sense algebraic -- like the one linked and the popular about Pythagoras. Once you pull our your ruler and measure you are obviously lost. Every result should be algebraic, not visual, but it's fine to express the algebra in figures instead of letters.

What do you mean “end up believing” are you insinuating that the shown example isn’t true? It very much is true. The reason it’s true might initially be confusion to you as a viewer because you have a difficult time telling the difference between 3/8 and 2/5 and assume the triangles have identical slopes, but the visual proof very much and truthfully shows that this is not he case.