You are right that mentioning sending people back is odd. Hmm.
I haven't seen any protests about illegals though. I only see anti-fascist protests and Israel/ Gaza protests.
Universities generally don't police speech allowing all sides to protest.
Discussion
It's not odd. If you are following the war on the USA. They are arresting protesters and they are finding out that many of them are not even American citizens. They are being paid to show up to protests. This is why democrats loved open borders. They used illegals to enter the USA so they could show up at the protests and paid them through NGO and many other criminal activities.
Yes there is also American citizens within those protests who are foolish and just going along with the protests because they are not that bright but many of them are also bring paid to show up at the protests.
Americans have the right to protest and even tourists but they are only allow to peacefully protests. Once they start causing crimes like attacking others, burning things then it becomes and illegal protest.
The universities are allowing this type of illegal activities because they have been receiving extra funding to allow the protests and the majority of staff are leftists.
Their is a massive war going on in the USA and Trump is exposing all of this. Many Americans are quite asleep but it's going to get worse which will force them to wake up.
He had an executive order recently making protests against israel illegal. So now any such protest is illegal. Hence his wording.