Paper cannot be biased but an organization made up of people surely can. It is entirely possible for Twitter to be removing all kinds of pro-Erdogan messages or whatever, which might have made it biased. Erdogan's claim of bias is pure BS of course, but it is not something that is theoretically impossible.
Nobel medicine prize awarded for work on parasitic diseases (Reuters)
from the article: Turkey says Twitter is 'biased,' used for 'character assassinations'