If you verify the ISO is valid (do the verification on another box as well to be sure), validate the write of the ISO to media (you didn't mention any release so this step maybe automatically done for you and you can see results; or may require additional step) you should okay if you didn't skip any steps.
Did you
- grab Lubuntu from a legitimate web site?
- and install per directions?
https://manual.lubuntu.me/stable/1/Installing_lubuntu.html
manual for latest stable release as you didn't provide release details; adjust stable if using lts for example
There is nothing illegal with downloading an Ubuntu (or flavor of Lubuntu like Lubuntu) ISO, writing to media & installing it; though this is layman advice as we don't know your location/country & thus what laws apply to you; but licenses are available for all Ubuntu software if you look so you can actually check for yourself & your local region.
Note: If unsure which web site to download form, do not ask google unless you can peruse the results offered & pick the correct one (google offers a number of sites to download & many are fan or fake). If you want a Ubuntu flavor like Ubuntu you should go to Ubuntu.com and then go to the official flavor site for your download.