The figure refers to people living along the 70,000 km of EU coastline OR within coastal areas across 22 Member States (not only strictly on the coastline), and represents about 21% of the EU's total population.
The European Commission figure covers 22 EU Member States, i.e. the EU's coastal Member States; landlocked Member States are not included in the coastal-area count.
The MEP's framing (coastal communities filling up in summer and emptying in winter, youth emigration, exposure to erosion and extreme weather) is a qualitative characterisation not quantified in the sources, but it does not affect the numerical claim.