Other devices believe that 10.0.3.144 is part of the network. The 255.255.255.255 subnet mask (a.k.a. /24) specifies the network size of 256 addresses. With the way that subnets are laid out, the 256-address subnet that contains 10.0.3.2-10.0.3.10 is the subnet that goes from 10.0.3.0 through 10.0.3.255. So, when other devices try to communicate to 10.0.3.144, then that address appears to be part of the same subnet. As a result, other devices will try to communicate using Layer 2 (ARP, Ethernet/WiFi), not Layer 3 (routing using IPv4/IPv6).
The computer which receives the Layer 2 traffic is recognizing 10.0.3.144 to be part of a subnet that it uses. So the computer pays attention to the traffic, which is addressed to the computer. Perhaps at a later point, the computer might even realize that 10.0.3.144 is an IP address that is on the other NIC. Because Networking is implemented with different software components, designed to handle one or more of the "layers" of the OSI model, it is entirely possible that the component which recognized 10.0.3.144 to be a Layer 3 IP address is not the same set of instructions/code/programming that determined that the ARP address was acceptable.
Understand that computers do not typically have system-wide IP addresses. Network ports have IP addresses. So each network card typically gets its own IP address.
If you don't want the second network card to be receiving traffic, you may need to do one or more of these things:
- set the IP address to be part of a different subnet. (Seeing a Variable Length Subnet Mask ("VLSM") chart may help to visualize what addresses are part of what subnets. The common charts typically just focus on the last octet, making the charts easiest to understand for /24 - /32 networks (where the first 3 octets of the IPv4 subnet mask are ("255.255.255").
- Disabling forwarding may be helpful. I think different computers may act differently about whether traffic to a different NIC, on the same system, is considered to be "forwarding". If forwarding is enabled, then there should be even less surprise that traffic may have reached another NIC.
- Firewalls may be useful for blocking some types of traffic. (Note that some firewalls may be limited. For instance, I happen to know that in OpenBSD, the DHCP client uses BPFs which don't get blocked by the IP firewall.)
To answer another question: Bridging can often be thought of as "Layer 2 forwarding". Layer 3 forwarding could also result in the traffic crossing to another NIC, even if you're not using Layer 2 bridging.
Regarding whether you can rely on the behavior: I believe so. But you should understand it, and ask questions until you do. Once you understand how things ought to work, you can verify if that is how things are working; if so, it ought to be rather reliable. If there are still mysteries, then surprises may be likely, so do be sure to keep asking about whatever is still unclear.