I think they mean to say that the contract does not the have a minimum term / tie-in that many others have. But saying "no contract" has specific meaning. It is quite valid to create an agreement that is "not intended to create a contractual relationship".
Agreements do not have to be a contract, it is just assumed that most are unless otherwise stated. There are exceptions - domestic arrangements are usually not, so my saying "If you wash the dishes I'll give you extra pocket money" to your kids is not legally enforceable as a contract.
The main difference between an agreement and a contract is that a contract is legally enforceable via the civil courts, and a non contractual agreement is not, it is said to be bound by honour only.
Bets with a bookie never used to be contracts by default (that may have changed). Oddly, postal services from Royal Mail are (apparently) not supplied under a contract.
Non contractual agreements can be very sensible in many cases - usually where the primary remedy if one party breaks the agreement is that the other party also does not do what was agreed, and both sides are happy that there is no further remedy required.
So, advertising, say, internet service, on TV with "no contract" is dodgy in many ways. For a start, anyone that does understand may find it rather a concern that a company would not be enforceably bound to provide the service they offer. However, it it rather nice that the customer is not enforceably bound to actually pay for it either. They say "terms apply" in the small print, and that is not entirely inconsistent with not being a contract - an agreement can have terms - just not enforceable ones.
If I got such a service, and did not comply with their terms, and they took me to court, I would simply point out that as per their advert the agreement was clearly not intended to create a contractual relationship and so there is no case to answer. No idea what a judge would say, but they should understand the principles of contracts and non-contracts well enough.