You might check your monthly prices. Some airbnb reductions, especially if you don’t adapt the default percentages, result in very low prices for some periods.
That leads to your listing being shown to a different clientele in a search for long term. An expensive place for 4 nights may be affordable for 50 to their budget. They may also believe, as it is still available for 50 nights, that you are desperate to rent it for much less even.
If you want to do only higher prices for shorter stays, you will get bookings much closer to the arrival date. Some guests looking for longterm don’t understand that.
As for the request to contact them outside airbnb, it can be a harmless newbie suggestion or an invitation to pay outside the system, usually to save the fees and press you on the price even more. (Or a scam, where you bever get the money or your house is trashed without insurance)
Just explain the system, insist on much more information to even consider the request and you will see if they comply or move on. If they move on, you can flag the profile. It may still be a newbie giving up when it gets complicated, but if it’s a scammer who gets more flags, airbnb may realise it.