Question says RYG should in sequence but does not say that G should be followed by Red or Yellow.
The 18th tile in the row is not yellow.
May mean 18th tile is Red or Green so not sufficient.
The 19th tile in the row is not green.
May mean 19th tile is Red or Yellow so not sufficient.
Combining Both Statements:
Says 18th is Red then we have R Y (also fulfilling second statement that it is not green)
Says 18th is Red then we have G, then at 19th we can have Either R (also fulfilling second statement that it is not green)
So there is no definite answer.
That's the trick.. the sequence could be G, Y, R, G, G, G...
OA is E.