Good plan to reduce risk usually is to diversify it.
Firstly (although not directly asked), you may want to reduce your dependence on oil for heating. So for example invest in better heating insulation, buy a Heat pump for backup, perhaps some solar panels etc.
That way, even if oil prices skyrocket even more (even as high as to become unaffordable to you; or even if the situation happens that there is not enough oil to fill the demand), you could still get by without it.
Secondly, split the risk in oil price change. So you may (for example) buy 50% of the oil now, and 50% later. So even if the price later goes up by 40%, you'd only be hit by 20% increase (but similarly, if the price goes down 20%, you'd only save 10%). Of course you can choose other ratios instead of 50-50 (depending on how comfortable you are to price volatility) as well as buy it in more then two installments (but note that there is extra cost to each installment)
As for the theoretical forecast:
What are some possible reasons that a heating oil rep would be anticipating oil prices falling?
Firstly, the person might be lying, either to increase their company profits, or to avoid spreading panic leading to their demise (for example, if they don't actually have enough oil to sell).
Or, they could be speaking their true belief, based on many economic analyses. That would likely get more extensive on economics SE or politics SE. There are many possible reasons: supply and demand (and many countries involved), possible government measures, weather forecast, estimates of political (de-)escalation with Russia, and other more-or less crystal-ball attempts of predicting the future.
You could ask them why they expect such price changes, and then you'd have one more datapoint to do research on and eventually decide on your tactics. (for which I've suggested relatively safe methods above)
But note: vast majority of such predictions would always be proven wrong -- as there is only one outcome that would come true, and all others would be shown as false. It might depend on how good economic analytics the person you spoke to was (although if they were good at it, I'd suspect they would be working in economic forecast sector instead), but what would actually happen to prices it is likely to be based more on your luck than on all forecasts in the world.
Basically, treat their advice in no higher regard than if your favorite news portal recommended you that now is the time to buy (or sell) Tesla or Apple stock, or sell (or buy) Bitcoin.