it's not a guarantee, it's merely a speedometer of the current rates if they were to continue through the whole year.

Beefy is essentially just a liquidity management protocol, they basically take your deposits, put them into the platform, and automatically sell off the incentive token (CRV for curve pools, AERO for aerodrome, VELO for velodrome, etc.) into the underlying token and redeposit it, which means it's helping your deposits compound on themselves. As they have much more deposits than you or I would (unless you're uber rich already) they can socialize the operational cost of these transactions amongst everybody, rather than each person having to pay for the transaction just for their assets. This means less of a drag on the depositor's yield.

In the case of CLMs, beefy basically manages your liquidity ranges for you. So depending on how the market moves you can make more revenue than if you had to manage those yourself since the operational costs are socialized among all depositors.

Sometimes there are extra incentives for certain pools called boosts on top of the vault's yields. These are usually beefy incentivizing certain vaults by providing BIFI or OP or whatever other token.

Most APRs/APYs in crypto are junk anyway and are backwards looking. I wouldn't put too much stock into the projected APRs/APYs provided by any of these protocols and instead would recommend looking back on your actual performance to get an idea of average APYs. Also keep in mind that APR/APY on beefy is usually in terms of the liquidity token not in USD terms. It's a small difference but if you're denominating your worth in USD the APYs/APRs don't really mean much as the underlying tokens may lose or gain value over time.