Trump’s comments on the surface are indeed outrageous.
However, note that police can detain people and hold weapons for a short period without a formal arrest while an investigation is being performed.
Also note that there can be removal of weapons without the owner of the weapons having a say beforehand. This happens a lot with protection from abuse (PFA) orders. Yes, there is a warrant to remove weapons, but the owner doesn’t get a say before the judge until a later hearing.
I think President Trump will be told by enough people around him that his words need to be “clarified.”