Since there hasn't yet been an inspection, there is no way anyone- you included – can tell what has caused these cracks. It could just be coincidence or it could be caused by vibration or movement in a part of your unit not directly connected.
I would write a polite letter to the Strata Manager saying that you don't believe the problem was caused by work on your unit but you will abide by the results of any test by a properly qualified and independent surveyor.
Regarding the sale of the unit, if this issue has been discussed at and EC meeting or the Strata Manager has made notes relating to it, references to it may appear on a thorough search by interested buyers. But it could just as easily slip under the radar.
It's still very much a case of buyer beware but now that the matter has been raised with you, the Owners Corp could pursue you for damage to common property and, if they are very, very quick, could even apply to put a hold on part of the proceeds of the sale (admittedly, this is very unlikely).
As I said, your best plan is to play this with a straight bat: tell them you don't think it's your problem but agree to pay for reasonable repairs if they can prove it is. If that IS the case, your builder's insurance might cover you if you can show that they did something they shouldn't have that caused the problem.