Something weird happened

something weird happened i was playing minecraft 1.17 now (yesterday it was out) and i was playing survival and i found mineshaft and i was like "cool i can get good stuff" but then i saw room and in that room was generated chain block and i was little confused and wanted ask someone if they know that if in 1.17 was update in mineshafts because i think that chain block was only in nether bastions

and sorry i cant send proof because i dont have wifi i have datas but trust me it happened