I'm not sure. I can feel alone for long periods of time without feeling lonely; but I can also be in groups of people and feel alone but without feeling lonely.
So this person is saying that they feel lonely while they're in groups of people. Now feeling alone and feeling lonely are two different things. Maybe this is a challenge for this person. When they're in retreat, when they're alone, they are restricted from talking to others, they essentially have no choice to actually interact with other people. Therefore they go into silence themselves, they do their meditation, they know they're alone, but they don't feel lonely because they're busy doing something. Maybe later, when this person is in a social gathering and they know that they are different from everybody, and nobody really wants to talk to them, even though there are ten, fifteen, maybe a hundred people around and nobody wants to talk to them - and they are wanting someone to talk to them - maybe that's what's causing them to feel lonely because they want interaction with other people. When you are in retreat and you don't want interaction with other people and you're comfortable with it, then you won't feel lonely because you feel comfortable being alone. But some people when they're in a group and they want the interaction, and they don't get it, indeed in those times they could feel lonely because nobody is talking to them.
This loneliness comes from obscurity, not having some fame, not having people look at us, talk to us, appreciate us, and so on. And definitely there are a lot of people who would feel that type of loneliness even though they are in a big crowd of people. But if you can develop contentment to actually be with who you are, and not want so much the attention from other people, then that will help you when you're in crowds to not to feel lonely, although you may feel alone, there is that difference.