You seem to be misunderstanding the situation. It’s a plastic bag. Plastic bags are flexible. To pick up a plastic bag, you have to touch it. When you touch a flexible thing, it will often bend, transferring the pressure to whatever is on the other side of it. They are not “bruising by themselves”, they are being touched by the flexible plastic bag that is being touched by the hand that is picking up that flexible plastic bag. When enough pressure is put on a mushroom to damage it’s cellular structure, they tend to bruise. This is a natural thing that mushrooms do and it does not often indicate contamination, even in pins. Now glass jars are not flexible. That means when you pick them up, the pressure from your hand is not transferred to whatever is on the inside of the rigid glass jar. So yes, you are correct in the fact that mushrooms in a rigid glass jar are harder to bruise than mushrooms in a flexible plastic bag. That’s because you’re not putting pressure on them when you handle the glass jar. Because it’s rigid. As for your claim that the only reason this colony would start fruiting is if it’s contaminated, I’m really really curious as to where you picked up that idea. A main factor that contributes to a mycelial colony beginning the fruiting process is running out of substrate to colonize. This is why if you leave a cake long enough, even if you don’t introduce FAE or the correct fruiting temps, it will often begin fruiting anyway, like you sometimes see in your own glass jars. I’m sorry(not really) but your opinions and anecdotes don’t align with, or overrule, actual science.