Yes, you should enter the income as Other income, it isn't self-employed income, since your husband didn't actively participate in the business in 2020. You'll have to pay tax on the gain on the sale of capital assets (partnership interest in your case).
To figure the gain, you need to know your basic in the asset. It is unclear from your question if your husband hold the 1% interest less that a year or more than a year. If it's short term, it is taxed as ordinary income, and if it was more that a year, it should be taxed as capital gain.
