Actually S10 is a shorter season. This season lasted all of 79 days.
S1 - 90 days, S2 - 98 days, S4 - 84 days, S5 - 63 days, S6 - 105 days, S7 - 98 days, S8 - 63 days, S9 - 84 days, S10 - 79 days. So on average a season lasts 88 days (rounded up). S10 falls just short, being the 3rd shortest season.
If anything they extended S10, rather than delayed S11. However it makes sense when you take into account the Chinese release date.