What the ALDE leader actually said is that it would be (relatively) easy for Scotland to apply and join the EU. He did not say it would e automatic.
Imho, the only way Scotland could automatically remain
in the EU is if the UK officially divided into two or more parts before
Article 50 is triggered, something which is not going to happen or May
allow it, Scotland would have to gain independence from the UK which is
not the same thing, it would not inherit any of the UK's rights.