The fact that there is a K-1 from a fiduciary income tax return with income allocated to the beneficiary is an indication that the beneficiary has taxable income from that state.
I'm in CA and the CA is very explicit. I believe most states K-1s do show the income is from a "domestic" source (note: in this case, "foreign" means another state, "domestic" means within the state).
Here's a link to the CA K-1, as you can see, the last column specifically reads, "California source amounts and credits"
https://www.ftb.ca.gov/forms/2022/2022-541-k-1.pdf
I just looked at the Massachusetts Form 2 a Form 2K-1. It doesn't have such a column, so unless the Trust/Estate provides the beneficiary with a K-1 from another state, it would be safe to assume that the income is from Massachusetts. It doesn't hurt, however, if you specifically inform the beneficiary that all the income are from within the state.
From MA
https://www.mass.gov/doc/2k1instrucionspdf/download
Nonresident Beneficiaries
If the beneficiary receiving income from an estate or trust is a nonresident of Massachusetts,
Massachusetts will only tax the beneficiary on income that is derived from Massachusetts sources. Where
an estate or trust derives income from both within and outside Massachusetts, it will be necessary to
determine what portion of the beneficiary’s share of income is from sources within and outside
Massachusetts so as to properly allocate and report the income on Schedule 2K-1.
