Is there a reason this is a big deal to you?
Acts 21:23-24 CSB17
"We have four men who have made a vow. Take these men, purify yourself along with them, and pay for them to get their heads shaved."
Numbers 6:13-15 CSB17
"“This is the law of the Nazirite: On the day his time of consecration is completed, he is to be brought to the entrance to the tent of meeting. He is to present an offering to the LORD of one unblemished year-old male lamb as a burnt offering, one unblemished year-old female lamb as a sin offering, one unblemished ram as a fellowship offering, along with their grain offerings and drink offerings, and a basket of unleavened cakes made from fine flour mixed with oil, and unleavened wafers coated with oil.”"
Do you think that Paul did not know what he was doing in keeping a Nazarite Vow?