Whether you depend on the income or not is irrelevant. Whether you did it once or many times is irrelevant. Whether you normally do it or not is irrelevant. You engaged in an income-producing activity and received actual income. Such an activity is rightly subject to the SE tax. Many self-employed people receive no 1099-MISC. You are required to claim your correct expenses.

If you were driving a race car, you might perhaps classify it as a hobby. Installing computer systems is not a hobby activity.