.. also, as far as I can make out, it wouldn't even slam into the frame of the window on the LH side .. the three windows seem to be staggered (not sure how to explain this) .. ok, you've got the one on the LH side which is innermost and slides across to the right over the centre panel on the bathroom side from what I can make out of it (can't seem to find a really clear, crisp image) .. then you've got a fixed centre panel, then you've got the panel on the RH side which slides across to the left on the outside over the centre panel. I'm presuming there must be some kind of mechanism to stop the window sliding any further, but it's not a frame and it's not the other (LH) window.
The other thing that never rang true to me was why OP thought an intruder would even think they would be able to get through a closed bathroom window in the first place, without having to smash the glass to either release a catch or undo a lock or a bolt .. they simply wouldn't bother, imo, and would gain access downstairs. Or, the only way they would bother to gain access through a bathroom window would be if it was already open, but it wasn't already open, not in OP's testimony it wasn't, anyway. So on all counts, the 'intruder - hearing the bathroom window slide open' story fails. No, 'an intruder' is not the immediate thing anybody is ever going to think if they hear a bathroom window opening (that's if it even did, anyway, which I very much doubt .. I think OP opened it later) .. first it would flash across their mind that no-one could open that window from the outside anyway and second it would flash across their mind that the most likely cause of the noise is the person who is sharing that room with you. BS, the lot of it!