It's the language being used.
Yes, they do come from other countries.
Words like swarm, invasion, illegal are used
Associating certain behaviours with the people who come over in boats.
Certain media outlets are very happy to highlight when they break the law in the most horrendous way but don't highlight positive things very much - all to create an impression in people's minds.
We have seen the images used before in the media and in political adverts
Repeated use of "the people, the British people" - as if we are all of one mind
Use by the media of phrases like "Enemies of the people"
This is how you divide people, create enemies and create other.
It's very effective.
If people pay attention to the rhetoric being used - and not just in that speech but in other speeches, interviews, videos etc, you will hear this language and this approach being taken.
From someone who has been described as a "left wing ,Remainiac, woke snowflake"