Is there any scenario where a exported (.sql) database dump could be bigger in size, than the database itself?
Lots of cases...


VARCHAR needs 1 or 2 extra bytes for the length; as text it needs two quotes, a comma, and possibly some escape characters.
The BIGINT 123456789012345 takes 8 bytes in the table, but 16 in the dump (15 digits, plus a comma).
A NULL value dumps as 5 bytes, regardless of what the datatype needs, which is probably 0.
DECIMAL(11,2) with -123456789.12:  5 bytes in the table -> 14 bytes in the dump
(and the DATETIME/TIMESTAMP example given in a Comment)


Going the other direction:


BIGINT 1:  8 bytes -> 2
CHAR(100) 'x':  100 characters -> 4 bytes.  (This example varies with charset, version and engine.)
DECIMAL(11,0) with 0:  4 bytes in the table -> 2 bytes (0,) in the dump


Etc.