It is a tremendous achievement that your son has purchased a house as a result of his own hard work and you are rightly proud.
When his fiancée commented that she was excited about it being their marital home and the start of a new chapter together, you took this as her trying to muscle in on your son’s achievement. This may be true. She could just as equally have been expressing her excitement over this next step in their lives and wishing to have it acknowledged as their new home together. She may have felt overlooked in that respect by your original post.
It would have been wiser, having not mentioned her in the first instance, to leave her comments on your post there. They are her words, not yours. Deleting her comments is very unusual. At best, you have come across as overly protective; at worst, as vindictive.
You cannot control how the world perceives your son and his achievements ad infinitum. And you cannot afford to lose the good grace of your future daughter in law if this is who your son has chosen to spend his adult life with. Going about things this way, you risk alienating them both - and jeopardising your involvement with any future grandchildren.
If it is possible to edit the post, I would acknowledge you are proud of your son’s hard work in buying his first home, delighted that it will be the place where he and his future wife get to start this next chapter of their lives, and wish them all the best in making very many happy memories together in their new home. That, with a heartfelt apology, may salvage the situation.
Going forwards, you want to be careful of setting your future daughter in law apart from your son in the way that you intended to this time round - for your own sake and theirs. That only places you at more of a distance from him as his life as a husband and family man evolves from here. You will find yourself slowly shut off from them and they from you. That doesn’t have to happen if you work hard to adjust your perceptions from now.