the short answer is that the statement is wrong. bitcoin will cease to exist without the internet.

the long answer is that it depends on what you mean by "an attack on the Internet infrastructure".
if it is just one nation restricting its people, cutting them from the internet,... then it will be different, people can still find alternative ways to connect to the bitcoin network (one of which is using satellites) and sync successfully.
but if it is global for whatever crazy reason, then bitcoin can not exist because it works right now because everyone can connect to anyone they want from anywhere in the world and also everyone can get in sync with the current state (new blocks and mempool) within seconds all thanks to the internet. alternative ways means you are connecting to a centralized place (such as the satellite) and you rely on that to be honest not to mention that it can have a lot of delays. so unless the day that every average Joe could launch his own satellite in orbit, bitcoin can't rely on such methods.