No, it's advising that it's not the most practical solution for what the OP wants, because it's too hot once you start moving around, bulky, not actually that waterproof and lacking a decent hood.
So people don't spend a lot of money on something that doesn't do the job they want it to do.
In the OPs case, it sounds like she has a suitable coat for wet weather, and when it's not warm enough, all she needs to do is layer up underneath, so if she's buying anything, she might do better with base layers (eg Uniqlo Heatech, M&S also have good ones) also a lightweight puffa jacket or fleece, the puffa jacket being an especially good choice because if you end up being too warm, you can take it off and stuff it in your coat pocket.
But if she wants to go out and buy a dryrobe because she's seen other people wearing them around town, she's free to do that and find out for herself why people are saying it probably won't be suitable for walking around in weather that's wet, windy and not particularly cold.