Mat 5:18 For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished.
Mat 5:19 Therefore whoever relaxes one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever does them and teaches them will be called great in the kingdom of heaven.
Elder, notice that Jesus says not an iota or a dot will pass from the law until all is accomplished.
The passage then expands on not just the ten but also vows, eye for eye, etc. which are not from the ten commandments, but are from the law. He uses the same "you have heard" formula to introduce them.
James also indicates breaking just one point means you have broken the whole law:
Jas 2:10 For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all.
In that same passage, as already outlined, he quotes from Deuteronomy on partiality and on the law of loving your neighbor. So this principle covers more than the ten commandments, yet some of the ten are also referenced.
Which law was it that James and the believers in Jerusalem were keeping?
The WHOLE law. Including ritual vows. Including sacrifices. Including temple worship. Including circumcision.
Act 21:20 And when they heard it, they glorified God. And they said to him, "You see, brother, how many thousands there are among the Jews of those who have believed. They are all zealous for the law,
Act 21:21 and they have been told about you that you teach all the Jews who are among the Gentiles to forsake Moses, telling them not to circumcise their children or walk according to our customs.
Act 21:22 What then is to be done? They will certainly hear that you have come.
Act 21:23 Do therefore what we tell you. We have four men who are under a vow;
Act 21:24 take these men and purify yourself along with them and pay their expenses, so that they may shave their heads. Thus all will know that there is nothing in what they have been told about you, but that you yourself also live in observance of the law.
Act 21:26 Then Paul took the men, and the next day he purified himself along with them and went into the temple, giving notice when the days of purification would be fulfilled and the offering presented for each one of them.