added article through GUI

there are about 300 tables in our replication,  i added one table through GUI,(replication monitor), then start Snapshot agent, will this reinitialize  all the table or just one newly added table.

i am using SQL 2008 R2 publisher, distributor SQL Server 2012, after started snapshot, it started reinitialize , is it because of , added table through GUI instead of script

thanks

V