Tight Muscles - tight muscles are existing in a shortened, contracted state. They cannot fully elongate. A person with muscles like this may not be able to, say, bend over and touch their toes. They need stretching
Tense Muscles - tense muscles can exist in a body that is very flexible and does not need stretching. In this case, the person might be able to say, bend over and touch their toes, but if you feel the muscles, they are holding a lot of tension. In this case they need to be "massaged" - compression, compresses, beating, this kind of thing. These muscles do not need stretching.
We have this fallacy that if someone is flexible, then all is good - but in truth, even yoga instructors who can bend l like Gumby can still have very tense bodies. So we have to learn to feel the tension in the muscles, and not base all diagnosis on flexibility and range of motion. Feel the tissue.